Semiconductor device dies are affixed into device packages for protection and for more convenient installation into an end use device. Device packages may be made of any suitable sturdy and resilient material, such as ceramic, glass, or plastic. The semiconductor device die is affixed to its package in a variety of manners, including the use of epoxy, solder, or brazing.
Various semiconductor-based devices are configured to detect physical events and/or cause physical events. Such devices are generally known as a Micro-Electro-Mechanical Systems (MEMS) device. For example, a MEMS gyroscope may be used to determine angular rotation and a MEMS accelerometer may be used to sense linear acceleration. The MEMS gyroscope and accelerometer measure rotation and acceleration, respectively, by measuring movement and/or forces induced in one or more silicon proof masses mechanically coupled to and suspended from a substrate, typically glass, using one or more silicon flexures. As another example, a MEMS motor may be used to induce or sense movement in a rotor.
A number of recesses etched into the substrate of the MEMS device allow selective portions of the silicon structure to move back and forth freely within an interior portion of the MEMS device. A pattern of electrical connectors, also known as metal traces, are formed on the MEMS device substrate to deliver various electrical voltages and signal outputs to and/or from the MEMS device. The MEMS device, after fabrication, may be affixed to a support structure, such as a device package, with electrical connection of the MEMS device bonded to corresponding electrical connections of the support structure.
For example, the support structure may have wire leads or connectors that provide connectivity between the outside surface of the support structure and the metal traces of the MEMS device. A flip chip bonding process affixes the MEMS die to its support structure while bonding of the metal traces of the MEMS device with the wire leads or connectors of the support structure.
Another type of support structure is a leadless chip carrier. After the MEMS die is affixed to the leadless chip carrier, external wire bonds are made to electrically couple connections of the MEMS device with traces on the leadless chip carrier or with connectors to other electrical devices.
MEMS devices may be very sensitive to inducted stresses and/or changes in orientation of the MEMS device components. Very small changes in stress and/or orientation of the working components of the MEMS device may significantly change the signal output of the MEMS device. Accordingly, prior to use in the field, the MEMS device is calibrated. Typically, calibration of the MEMS device is performed at the factory or during a field calibration process. For example, output of a stationary MEMS gyroscope or accelerometer should be null (zero). Accordingly, during the MEMS device calibration process, the output of the stationary MEMS gyroscope and accelerometer is referenced to a null value and/or is electrically compensated to a null output.
Such “hard mounting” of the MEMS die to the support structure results in the MEMS die becoming solidly, or rigidly, affixed to the support structure. Temperature fluctuations of the device package and/or the MEMS causes thermal expansion (during heating) and/or contraction (during cooling) in the support structure. However, since the materials of the device package, the MEMS die, and any bonding material therebetween, are different, the relative amount of expansion and/or retraction will be different for the support structure, the MEMS die, and any bonding material therebetween. This differential expansion and/or differential contraction during a temperature change may induce changes in the orientation and/or stress of the working components of the MEMS device. Such differential expansion and/or differential contraction during a temperature change may result in the MEMS device becoming uncalibrated.
Further, some materials do not return to their original size and/or shape after a temperature cycle. For example, a gold ball bond may be used to affix the MEMS die to the support structure. Because of the ductility of the gold ball bond, a temperature-induced deformation causes a nonelastic deformation of the gold ball bond. Accordingly, after a number of temperature cycles, the gold ball bond does not return to its original pre-deformation form and/or stress. Such nonelastic, hysteresis deformation of the gold ball bond may result in the MEMS device becoming uncalibrated.
Accordingly, it is desirable to isolate the MEMS die from changes in orientation and/or stress that may occur as a result of differential expansion and/or differential contraction during a temperature change, and from hysteresis deformations resulting from temperature cycles. One prior art technique is to dispose an isolating structure between the MEMS die and the device package. For example, a plate, a pad, or the like made of a relatively thermal expansion resistant material may be bonded to the MEMS die and the device package. However, such intermediate isolating structures may not be entirely effective as movement and or stresses may be transferred through the isolating structure to the MEMS die. Further, such intermediate isolating structures may be relatively complex and expensive to fabricate and install between the MEMS die and the device package.
U.S. application publication 2002/0146919 for the application entitled “Micromachined Springs For Strain Relieved Electrical Connections To IC Chips,” to Michael Cohn and filed on Dec. 31, 2001 (which is incorporated herein by reference in its entirety), illustrates an exemplary system to alleviate the effects differential expansion and/or differential contraction during a temperature change, and from hysteresis deformations resulting from temperature cycles. However, the Cohn system is extremely complex since it is made during device fabrication, and employs overplating of a series of metals to provide spring properties.
U.S. application publication 2004/0147056 for the application entitled “Micro-Fabricated Device and Method of Making,” to James McKinnell et al. and filed on Jan. 29, 2003 (which is incorporated herein by reference in its entirety), illustrates another exemplary system to alleviate the effects of differential expansion and/or differential contraction during a temperature cycle. However, the McKinnell thermal isolating structure has a very complex shape and a specific length requirement. Accordingly, the McKinnell thermal isolating structure is relatively difficult to form and to place in its installed position between the micro-fabricated device and the device substrate.